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Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50μm they can incorporate smooth muscle and are known as muscular venules. [1] Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. [2]
The venous system apart from the post-capillary venules is a high volume, low pressure system. Vascular smooth muscle cells control the size of the vein lumens, and thereby help to regulate blood pressure. [31] The post-capillary venules are exchange vessels whose ultra-thin walls allow the ready diffusion of molecules from the capillaries. [10]
These substances pass through capillaries through three different systems or mechanisms: diffusion, bulk flow, and transcytosis or vesicular transport. [3] The liquid and solid exchanges that take place in the microvasculature particularly involve capillaries and post-capillary venules and collecting venules. [citation needed]
High endothelial venules (HEV) are specialized post-capillary venules characterized by plump endothelial cells as opposed to the usual flatter endothelial cells found in regular venules. [1] HEVs enable lymphocytes circulating in the blood to directly enter a lymph node (by crossing through the HEV).
The capillaries connect to venules, and the blood then travels back through the network of veins to the venae cavae into the right heart. The micro-circulation — the arterioles, capillaries, and venules —constitutes most of the area of the vascular system and is the site of the transfer of O 2, glucose, and enzyme substrates into the
Blood viscosity is the thickness of the blood and its resistance to flow as a result of the different components of the blood. Blood is 92% water by weight and the rest of blood is composed of protein, nutrients, electrolytes, wastes, and dissolved gases.
The common sense is where this comparison happens, and this must occur by comparing impressions (or symbols or markers; σημεῖον, sēmeîon, 'sign, mark') of what the specialist senses have perceived. [16] The common sense is therefore also where a type of consciousness originates, "for it makes us aware of having sensations at all". And ...
It appears that different signaling pathways regulate the constriction of capillaries by pericytes and of arterioles by smooth muscle cells. [31] Recent studies on rats have found such a signaling pathway in which after spinal cord injury and induced hypoxia below the injury, there is excess activity of monoamine receptors on pericytes which ...